Apparatus for perforating well casing and the like



Sept. 30, 1958 H. s. ROBERTSON 2,853,944

APPARATUS F OR PERFORATING WELL CASING AND THE LIKE Filed Feb. 6, 1951 v 3 Sheets-Sheet 1 E i FIGLI.

V HWI-:NTOFLA HARRY s. ROBERTSON HIS ATTORNEYS.

Sept- 30, 1958 H. s. ROBERTSON A 2,853,944

APPARATUS FoR PERFORMING WELL cAsING AND THF LIKE Filed Feb. 6. 1951 3 Sheets-Sheet 2 I/fa F`IG2A.

INVENTOR.

N O m R E B O R S Y R R A H l HIS ATTORNEYS.

Sept. 30, 1958 H. s. ROBERTSON 2,853,944

APPARATUS FoR RRRFORATING WELL cAsING AND TRF LIKE;

Filed Feb.v e, 1.951 s sheets-sheet s FIGB.

INVENTOR.

HARRY S. ROBERTSON A 2,853,944 Patented Sept. 30,y 1958 APPARATUSv FOR PERFORATING WELL CASING ANDv THE LIKE Harry S. Robertson, Houston, Tex., assignmtn Borg- Warner Corporation, Chicago, lll., a corporation of Illinois Application February 6, 1951, seranl No. 209,598

Claims. (Cl. 102-20) The present invention relates to apparatus for perforating well casing and the like, and more particularly to new and improved apparatus of lthis character which is capable of achieving a greater depth of penetration than has been possible, heretofore, with conventional perfo rating apparatus of substantially the same. lateral dimensions.

Perforating tools embodying conventional bullets or shaped explosive charges have beeny employed heretofore for perforating steel casing or the like of the type used to line oil wells drilled into the earth. While suchapparatus has been successful, restrictions imposed by the narrow confines of the casing have placed a definite limit upon the depth of penetration into the formations that can be obtained. While a greater depth of penetration than now attainable wouldv be highly desirable, no substantial increase in -the depth of penetration. beyond that limit has been possible with the perforatingtools previously available.

It would be highly advantageous to be able to perfo- `rate well casing after the narrow diameter tubing leading to the production equipment at the surface is set, since this would enable a relatively light fluid to be substituted for the heavy drilling mud normally used as a blow-out preventer, thereby forestalling any possibility of the perforations becoming sealed olfv by the filter cake formed by the mud. In the prior practice, this could not be done because no perforating tool small enough to pass through the tubing would have suicient power to penetrate the casing and surrounding cement into the formation. Hence, the casing had to be perforated before the tubing was set, and expensive drilling crews andA rigs had to remain idle pending completion of the perforating operation and of such tests as were required to be made subsequently thereto.

Further, upon completion of a well, a formation located at a level other than that where the casing was initially perforated, could' .not be produced without removing the tubing so as to permit a workover job to be done with conventional casing perforating means. Also, difficulty has been encountered in securing,` with present-day perforating tools, sucient penetration of a drill pipe to allow uid circulation therethrough as required occasionally to loosen a drill pipe that is stuck in a well.

It is an object of the invention, accordingly, to provide new and improved apparatus for perforating Well casing and the like which is capable of being lowered into a, bore hole through pipe of extremely small. diameter, but which has greater penetrating power than has been obtainable heretofore with tools of comparable diameter.

Another `object of theA invention is to provide new and 'improved perforating apparatus of the above character which is capable of perforating a bore hole casing of conventional size though mounted in a housing of exand improved apparatus for perforating well casing and the like in which the direction of penetration' into the formations is such as to facilitate drainage therefrom into the bore hole by gravity, thereby minimizing. any tendency of the perforations to becomeV plugged, and resulting in the perforation of aplurality of producing sections in cases where thin layers of shale are intercalated between producing sands.

A further object of they invention is to provide new and improved shaped charge perforating apparatus ofthe above character in which a more powerful shaped charge may be placed ina housing of given lateral' dimensions than has been possible heretofore.

These and other objects of the invention are attained in shaped explosive charge perforating apparatus by disposing one or more. shaped charge devices in a bore hole each with its longitudinal axis disposed atan angleto both the longitudinal axis of the borehole and a normal thereto. Preferably, the devices` are directed; upwardly so that the perforations. formed therebyl in the surrounding formations are directed downwardly. With thisl construction, it will be apparent that `a larger shaped charge device can be accommodated, and a stand-od distance can be more readily provided for in a bore hole orl casing of given diameter than would be the case if the devices were mounted. with their longitudinal axes normal to the longitudinal axis of the bore. hole, as in the prior art. Further, since theI perforations are directed. downwardly towards the bore hole, drainage of fluid from the formations into the bore hole is facilitated and there is less tendency for the perforations to become plugged.

Additional objects and Vadvantages of the, invention will' be apparent from the following detailed description of several typical embodiments thereof, taken in conjunction with the accompanying drawings in which:

Fig. l is a View of perforating `apparatus constructed according to the invention lowered through a string of tubing of very narrow diameter into a cased bore hole;

Fig. 2' is a partial view in longitudinal section of the apparatus shown in Fig. 1;

Fig. 2A is a side view of the means employed in the apparatus shown in Fig. 2 to retain the shaped charge devices in position within the housing;

Fig. 3 isa side view of another form of supporting meansl which may be employed to retainl the shaped charges in their relative positions within the housing;

Fig. 4 is a side view, partially in longitudinal section, of still another charge device supporting means which may be employed in accordance with the invention; and

Fig. 5 is a viewV of the cased bore hole shown in `Fig. l immediately after a perforating operation has been completed therein withl apparatus constructed accordingv to the invention..

By way of illustration, the invention will be described herein as applied to perforating operations in a cased bore hole in which a string of tubing has. been set. It is understood, however, that the invention can be applied with equal effectiveness in a wide variety of perforating operations including. the perforation of casing in a well prior to the setting of tubing therein and the perforation of drill pipe to en'ableit to be gotten free from the bore hole, for example.

In Fig. 1, a bore hole 10 has been drilled into the earth, passing through a formation 11 which has been determined by a conventional logging method, for eX- ample, to be potentially productive. One or more thicknesses of' steel casing 12 have been placed in the bore hole 10 and the formation has been squeezed off by means of cement 13 in the usual manner. Also, a string of tubing 15, which is generally of veryv small diameter, of.. the order of two.inches, for example, has been seein the well.

apparatus into the tubing 15, as, for example, the apf paratus shown in Figi of Ennis Patent No. 2,317,039.

Although Fig. 1 illustrates an original oil well completion job, it is understoodk that the same technique would be applied in the case of a so-called workover operation, i. e., one in which the casing in a completedk well is to be perforated at a level different from the level where the casing was originally perforated.

The perforating apparatus comprises a housing-16 small f enough in diameter to enable it to be lowered through the production equipment 14 and the tubing 15 to a position opposite the potentially productive formation 11. The housing 16 is adapted to be lowered into the bore hole by means of an insulated electric cable 17 which may be spooled at the surface by any conventional means, such as a winch (not shown), for example. Within the cable 17 are one or more electrical conductors 18 which provide electrical communication from the surface ofthe earth to the interior of the housing 16.

As shown in Fig. 2, the housing 16 is preferably cylindrical and suciently small in external diameter toenable it to pass through the tubing 15. It may comprise,

- for example, a hollow, imperforate, tubular body portion 47 and upper and lower closure members 19 and 40 which are designed to resist the pressure of any iluid that may be inthe bore hole 10, thus keeping the interior of the housing 16 dry. Preferably, the material of which the entire housing 16 is made should be sufficiently brittle to insure complete destruction of the housing 16 during the perforating operation. clude, for example, Pyrex glass, bell bronze, steel aircraft tubing, cast iron, or Securalloy. However, if desired,

the housing 16 may be manufactured from a strong material such assteel in order to enable it to resist destruction during the perforating operation.

Within the housing 16 are disposed a plurality of shaped explosive charge devices 20 which are mounted at an angle with respect to both the longitudinal axis of the housing and a normal thereto, preferably being directed upwardly. These devices may be of the type disclosed in the copending application (now abandoned) of Andre Blanchard, Serial No. 123,003, led October 22, 1949, entitled Shaped Charge Perforating Apparatus, for example. housing a hollow explosive charge 22 provided with a liner 23, the liner and container being of the flare counterare type disclosed in Fig. 6 of the aforementioned copending application. As there described, the sum of the apex angles of the outermost liner portion 23a and the outermost container inside wall portion 21a should be substantially equal to the sum of the apex angles of the liner portion 23h and of the container inside wall portion 2lb. Also, the container should be pressure resistant, i. e., capable of restraining by inertia effects the forces developed upon detonation of the explosive charge, the inertia elects being produced either by the mass of the container or by its tensile strength or by both.

Each of the devices 20 is adapted to be detonated Suitable materials may in- Each device 20 may comprise a container 21 from the rear by suitable means such as a primacord fuse 24 threaded through an opening 60 in the rear portion of the container 21. The primacord 24 may be detonated in any convenient manner, as for example, by a conventional electrical blasting cap 61 preferably mounted in the lower portion of the body 47, although it may be mounted in the upper portion, if desired. The blasting cap 61 may be set off bypassing electric current from a battery 26 and a switch 27 at the surface of the earth through the conductor 18 (Fig. 1). It is understood, of course, that any other conventional electrical means or mechanical means such as a go-devil, for ex- 4 ample, may be used to detonate the shaped devices 20 within the housing 16.

By virtue of the angular mounting described above, it will be apparent that a housing 1,6 of given diameter can accommodate considerably larger devices 20 than would be the case if the charges were mounted with their longitudinal axes normal to the longitudinal axis ofthe housing 16 in the conventional manner. Of primary interest, however, is the fact that the angular dispositionof the devices provides sufficient stand-olf distance between the mouth of each charge device 20 and the container 16 to insure proper formation of the jet before itk enters n the bore hole. n

The shaped charge devices 20 may be retained in the desired angular position by means of a plurality of sleeves 28 into which the containers 21 are adapted to fit snugly. The sleeves 28 are preferably supported on a plurality of rods 29, two being shown in Fig. 2A, also made of destructible material, to which they are soldered or otherwise attached. Also, the container 21 is provided with front and rear bearing surfaces 2li and 21r, respectively, which conform generally tothe contour of the inside wall of the tubular body portion 47.

In assembling the apparatus preparatory to lowering it into the bore hole, the devices 20 are inserted in their krespective sleeves 28.V An elastic band 41 or the like may then be placed around the lowermost portion of each container 21 to prevent the devices 20 from inadvertently slipping out of the sleeves 28. The primacord fuse 24 is then threaded through the openings 60-in the rear portions of the devices 20.k The entire assembly may then be inserted into the tubular body portion 47 of the housing 16 and the bottom closure member 40 made k secure thereto.` The primacord fuse 24 may then be connected to the blasting cap 61 (Fig. 1) which in turn is electrically connected to the cable conductor 18. The

upper closure member 19 is then secured in place whereupon the assembled perforating apparatus is ready for lowering into kthe bore hole.

It will be noted that the shaped explosive charge containers 21 as supported in the tubular body portion 47 engage opposite portions of the inside wall of the latter and thus constitute strengthening members for the tube.

In operation, the housing 16 is first lowered through the production equipment 14 at the surface to the level of the potentially productive formation 11. The switch 27 is then closed by the operator at the surface, thereby causing the primacord 24 to detonate the charges 22. The jets formed upon detonation of charges 22 penetrate the Wall of the housing 16 and cause a plurality of upwardly extending perforations 31 to be made through the casing 12, the cement 13 and into formation 11 (Fig. 5). By virtue of their angular course, the perforations 31 facilitate the drainage of fluid from the formation 11 into bore hole 10. As stated, the housing 16 is destroyed during the perforating operation and the pieces thereof drop harmlessly to the bottom of the bore hole 10, as shown in Fig. 5. Thus, the cable 17 may be readily retracted through the tubing 15 and the surface equipment 14 for attachment of another perforating assembly, if desired.

In order to avoid inadvertent discharge of the perforator while within the tubing 15, it is desirable to lowe1- into the bore hole with the housing 16 a device which will indicate clearly to the operator at the surface when the housing 17 passes out of the tubing 15 into the casing 12. A casing collar locator of the type disclosed in the copending application of H. C. Fagan, Serial No. 668,298, filed May 8, 1946, now Patent No. 2,558,427, which provides characteristic signals in response to magnetic anomalies in the well serving as depth markers therein, would be entirely satisfactory for this purpose.

Fig. 3 illustrates another form of means for retaining the shaped charge devices in the housing 16 in the desired angular position. In this embodiment, the container 21 of each shaped charge device carries a bracket 32 which lies in a plane including the axis of said charge device and is disposed perpendicularly to the outer wall of the container. In the bracket 32 is formed a hole 33 which is so placed as to lie in the center of the housing 16 when the charge device 20 is inserted therein. The container 21 also carries a second bracket 34 on the rear portion thereof opposite the bracket 32. The bracket 34 lies in the same plane as the bracket 32 and carries a pin 35 which is adapted to be inserted in the hole 33 in the bracket 32 of another container 21.

As in the embodiment shown in Fig. 2, the front and rear portions of the charge containers 21 are shaped to conform generally to the contour of the inside wall of the tubular member 47. Further, when the container 21 is inserted within the tubular member 47, these front and rear portions are adapted to engage opposite portions of the inside wall of the tubular member 47 and the free end of the bracket 32 is adapted to engage the inside wall at a location directly below the rear end of the container- 21. By virtue of this construction, the container 21 is maintained properly positioned within the tubular member 47 and serves as a strengthening member for lthe latter.

The bottom closure member 40 of the housing 16 may be provided with a bracket 32 having a hole 33 therein adapted to receive a pin 35 on a charge container 21. As may be seen in Fig. 3, by inserting the pin 35 on the bracket 34 of one charge container into the hole 33 in the bracket 32 of another charge container, a string of angularly directed charge devices is formed, each charge device facing at a 90 degree angle with the charge devices directly above and below it.

In the preliminary assembly operation at the surface, a plurality of charge devices are interconnected as shown in Fig. 3 and suspended from the bottom closure member 40. After threading the primacord fuse 24 through the holes 60 in the charge devices, the entire string of charge devices may be lowered into the inverted tubular body portion 47 of the housing 16, and the primacord fuse 24 connected to a suitable detonating device as mentioned above. The top and bottom closure members 19 and 40 are then sealed, whereupon the tool is ready to. be lowered into a bore hole. It will be noted that when the charge devices are inserted in this manner they are directed upwardly with respect to the bore hole. If it is desired that the charge devices be directed downwardly, they may simply be reversed prior to insertion in the housing 16.

The embodiment shown in Fig. 3 has several advantages. For one thing, the primacord fuse may be more expeditiously employed and does not pass so close to the charge containers as possibly to deform said containers before the jets can form. Further, more charge devices may be used for a given length of housing.

In the form of the invention shown in Fig. 4, each charge container 21 has secured near the base thereof a cylindrical ring 50, which is symmetrical about the axis of the charge device 20. The ring 5.0 carries a rod 5.1 which extends therefrom at such an angle that it will coincide with the longitudinal axis of the housing 16 when the container 21 is properly assembled therein. The lowermost portion of the rod 5.1 is fitted with external threads 52. At the forward outer end of the container 21 is mounted a second rod 53 which is also adapted to coincide with the axis of the housing 16 when the container 21 is properly assembled therein. Rotatably mounted at the upper Vend of the rod 53 is a sleeve 54 having internal threads adapted to iit the threads 52 on the rod 51. l

By threading the rod 5,1 on one container into the sleeve 54 on another container 21, a plurality of charge devices may be assembled together 'as in Fig. 4. By merely rotating any charge device 20 while maintaining thesleeve 5.4 on the charge device below steady prior tion with Figs. 2 and 3 to form the complete perforat-` ing tool.

`It should be noted that the ring-like members 50 which overlie the liners 23 are preferably symmetrically disposed about the axes of the charge devices 20, in order to minimize any possible jet malformation.

The invention thus provides novel and highly effective apparatus for perforating well casings and the like. By mounting shaped explosive charge devices in the housing with their longitudinal axes disposed angularly with respect to both the longitudinal axis of the bore hole and a normal thereto, more powerful charge devices can be accommodated within a housing of given diameter than has been possible previously. Further, by directing the charge device upwardly at an angle, the perforations made in the formation extend downwardly towards the bore hole, thereby facilitating drainage from the formation into the bore hole.

The several embodiments disclosed herein are obviously susceptible of modiiication in form and detail. For example, other means for supporting the charge devices in the desired angular position can be used provided that care is taken to insure that such means either does not overlie the liner for the charge device or if it does overlie the liner, that such means is symmetrically disposed about the longitudinal axis of the charge device. All such modifications are intended to be included Within the scope of the appended claims.

I claim:

l. Apparatus for perforating well casing or the like comprising a hollow elongated watertight' body adapted to be lowered into a well, a plurality of shaped explosive charge devices mounted in containers in said body, each of said containers having portions cooperating with portions of said body to support said containers with the longitudinal axes of the charge devices xedly disposed at an oblique angle to the longitudinal axis of the body, a plurality of brackets mounted on opposite sides of each of said containers, one of said brackets having a transverse opening therein and the other bracket carrying a transversely extending pin, the pin on the bracket on one charge device being fitted in the hole in the bracket of an adjacent charge device, and means for detonating said charges from the surface of the earth.

2. Apparatus for perforating well casing and the like comprising an elongated tube, closure members for the open ends of said tube, and a plurality of longitudinally spaced apart shaped explosive charge devices in said tube, each of said devices comprising a tubular container extending transversely of said tube and having a cavity therein facing the inside wall of said tube, an explosive charge in said cavity having a recess therein facing said tube inside wall and fitted with a liner, coupling means mounted on opposite sides of said container at locations lying along the longitudinal axis of said tube to facilitate coupling a container detachably to containers on opposite sides thereof in said tube, said devices being detachably coupled to one another in said tube by said respective coupling means, at least one of said coupling means including a stabilizing member extending transversely of said tube and having a free end forming a bearing surface engaging the inside wall of the tube to assist in supporting said container, means for detonating said explosive charges Iand means for initiating operation of said detonating means from the surface of the earth.

3. Apparatus for perforating well Icasing and the like comprising an elongated tube, closure members for the open ends of said tube, and -a plurality ofv shaped explosive charge devices in said tube, each of said devices comprising a container having a longitudinal axis extending transversely of said tube, means forming a conical cavity in said container facing the inside wall of said tube, an explosive charge in said cavity having a recess therein facing Said tube inside wall and fitted with a liner, lcoupling means mounted on opposite sides of said container and oriented differently with respect to one another to facilitate coupling a container detachably to containers on opposite sides thereof in said tube, said devices being detachably coupled to one another in angularly spaced apart relation about the longitudinal axis of said tube, at least one of said coupling means including a stabilizing member extending transversely of said tube and having a free end forming a bearing surface engaging the inside wall of the tube to assist in supporting said container, means for detonating said explosive charges and means for initiating operation of said detonating means from the surface of the earth.

4. Apparatus for perforating well casing and the like comprising an elongated, substantially imperforate tube, said tube being strong enough to withstand hydrostatic pressure in a well but frangible by the explosive forces generated in a perforating operation, closure means for the open ends of said tube,and a plurality of shaped explosive devices in said tube, each of said devices comprising a container having a longitudinal axis extending transversely of said tube and provided with a conical cavity therein facing the inside wall of the tube with its longitudinal axis xedly disposed at an oblique angle to the longitudinal axis of the tube, means forming a bearing surface `at the front end of the container conforming generally to the contour of the inside wall of the tube, means forming a bearing surface at the rear end of the container conforming generally to the contour of the inside wall of the tube, a stabilizing member secured at the front end of the container and extending transversely of the tube, the free end of said stabilizing member having a bearing surface engaging the inside wall of the -tube to assist in supporting said container, coupling means carried by said stabilizing member to facilitate coupling said container to an adjacent container, a laterally extending arm mounted on the side of said container opposite said stabilizing member, coupling means carried by said arm and oriented -angularly with respect to the coupling means on the stabilizing member to facilitate coupling said container to an adjacent container, said containers being coupled together by said coupling means in angularly spaced apart relationship about the longitudinal axis of said tube, means for detonating said explosive charges, and means for initiating operation of said detonating means from the surface of the earth.

5. Apparatus for perforating well casing and the like comprising an elongated tube, closure members for the open ends of said tube, and a chain of interlinked shaped explosive charge devices disposed in said tube between the end closure members thereof, each of said devices comprising a container having an elongated cavity therein facing the inside wall of said tube with its longitudinal axis xedly disposed at an oblique angle to the longitudinal axis of the tube, the front and rear ends of said container being shaped to tit snugly within said tube, an explosive charge in said cavity and having a recess therein facing said tube inside wall, said recess being coaxial with said container cavity, a liner for said recess, linkage members mounted on opposite sides of each container, one of said members carrying a pin and the other having pin receiving means, the pins of linkage members on certain of the containers cooperating with the pin receiving means of linkage members on other containers to form an interlinked chain of shaped charge devices in said tube, means for detonating said explosive charges, and means for initiating operation of said detonating means from the surface of the earth.

6. Apparatus for perforating well casing and the like comprising an elongated, imperforate, cylindrical tube,

closure members for the open ends of said tube, and a chain of interlinked shaped explosive devices disposed in said tube between the end closure `members thereof, each of said devices comprising a pressure resistant container having an opening therein including a forward, rearwardly converging opening portion of one apex angle communicating with another rearwardly converging portion of greater apex angle, the front and rear ends of said container being shaped to t snugly Within said tube with the longitudinal axis of said container opening xedly disposed at an oblique angle to the longitudinal axis of the tube, a liner in said container opening provided with a cavity therein facing the inside Wall of said tube having a forward, rearwardly converging cavity portion of greater apex angle than said forward container opening portion, and another rearwardly converging cavity portion of lesser apex angle than said forward cavity portion, said cavity portions being disposed coaxially with respect to said container opening and being positioned so as to be embraced by only converging portions thereof, the sum `of the apex angles of said container opening forward portion and said liner cavity forward portion being approximately equal to the sum of the 'apex angles of said another container opening portion and of said another liner cavity portion, an explosive charge in said container opening and in contact with said liner, linkage members mounted on opposite sides of each container, one of said members carrying a pin and the other having pin receiving means, the pins of linkage members on certain of the containers cooperating with the pin receiving means of linkage means on other containers to form an interlinked chain of shaped charge devices in said tube, means for detonating said explosive charges, and means for initiating operation of said detonating means from the surface of the earth.

7. A shaped explosive charge device comprising a hollow tubular container, means forming front and rear bearing surfaces on said container conforming generally to the surface of a right cylinder having a longitudinal axis disposed at a xed oblique angle to the longitudinal axis of said container, a laterally extending rigid stabilizing member formed on said container and having bearing means substantially at the surface of said right cylinder and spaced apart longitudinally of the axis of said right cylinder from the means forming said container rear bearing surface, and an explosive charge in said container, said charge having a cavity therein facing one end of said container and lined with a liner.

8. A shaped explosive charge device comprising a hollow tubular container, a pair of rigid members formed on said container and extending laterally on opposite sides thereofmeans on said rigid members facilitating connection of said container detachably to elements on opposite sides thereof at points spaced apart from said container on opposite sides thereof and lying along aline disposed at a fixed oblique angle with respect to the longitudinal axis of the container, means forming front and rear bearing surfaces on said container conforming generally to the surface of a right cylinder having a longitudinal axis substantially coinciding with said line, and an explosive charge in said container, Said explosive charge having a cavity 'therein facing one end of said container and lined with a liner.

9. A shaped explosive charge device comprising a hollow tubular container, a pair `of rigid members formed on said container and extending laterally on opposite sides thereof, means on said rigid members facilitating connection of said container detachably to elements on opposite sides thereof at points spaced apart from said container on opposite sides thereof and lying along a line disposed at a xed oblique angle with respect to the longitudinal axis of the container, means forming front and rear bearing surfaces on said container conforming generally to the surface of a right cylinder having a longitudinal axis substantially coinciding with said line, bearing means formed on one of said rigid members substan tially at the surface of said right cylinder and spaced apart longitudinally of the axis of said right cylinder from the means forming said container rear bearing surface, land an explosive charge in said container, said charge having a cavity therein facing one end of said container and lined with a liner.

10. A shaped explosive charge device as defined in claim 8 wherein said pair of rigid members comprises a pair of rods extending coaxially along said line disposed at said xed oblique angle with respect to the longitudinal `axis of the container; and wherein the means on said rigid members facilitating connection of said container detachably to elements on opposite sides thereof comprise an externally threaded portion at ythe end of one of said rods `and a sleeve rotatably mounted on the end of the other of said rods, said sleeve having internal threads complementary to said external threads and coaxially disposed with respect to said line.

References Cited in the le of this patent UNITED STATES PATENTS Prikel Dec. 31, 1935 10 2,228,623 Ennis Jan. 14, 1941 2,399,211 Davis Apr. 30, 1946 2,402,153 Elliott June 18, 1946 2,494,256 Muskat Jan. 10, 1950 2,543,814 Thompson Mar. 6, 1951 2,587,244 Sweetman Feb. 26, 1952 2,616,370 Foster Nov. 4, 1952 2,629,325 Sweetman Feb. 24, 1953 2,630,182 Klotz Mar. 3, 1953 2,639,770 Huber May 26, 1953 2,649,046 Davis Aug. 18, 1953 2,667,836 Church et al. Feb. 2, 1954 2,669,928 Sweetman lFeb. 23, 1954 2,682,834 Church et al July 6, 1954 2,687,823 Whitmore Aug. 31, 1954 2,708,408 Sweetman May 17, 1955 FOREIGN PATENTS 645,466 Great Britain Nov. 1, 1950 OTHER REFERENCES Article by W. T. Box and R. F. Meiklejohn, published in World Oil, volume 130, No. 4, March 1950, pages 112, 116, 118, 121, and 122. 

